Certain ethylenically unsaturated chlorinated hydrocarbons such as perchloroethylene are employed for cleaning and degreasing electronic components such as module substrates, assemblies, and printed circuit boards. However, at the operating temperature, such hydrocarbons such as perchloroethylene tend to react with water and/or oxygen contaminants to produce, in the case of perchloroethylene, trichloroacetyl chloride which may then subsequently hydrolize to hydrochloric acid.
The presence of chloride can be extremely harmful to the components contacted with the compositions. For instance, chloride can be very detrimental to circuitry resulting in "black fingers" on electrical contacts and thereby contributing to electrolytic corrosion on metalized ceramics. The term "black fingers" refers to corrosion of for instance tin and/or lead on the ceramic resulting in the corresponding chlorides.
In order to remove chloride from such systems, nitrogen containing inhibitors such as diallylamine have been added. The nitrogen compound such as the diallylamine is generally added periodically in order to combine with for instance the intermediate trichloroacetyl chloride and also with the by-product, hydrochloric acid.
Reactions nos. 2 and 3 hereinbelow illustrate the reactions when adding diallylamine to a perchloroethylene system: ##STR1##
The diallylamine hydrochloride formed from reaction Nos. 3, illustrated above is an insoluble precipitate in the perchloroethylene and it can thereby be removed in filters. However, it is still present in the system and is in equilibrium therein. If the filters are not changed periodically, more and more of the nitrogen compound (e.g. diallylamine) is needed to control the chloride concentration. Various different processes have been suggested for purifying liquids such as perchlorethylene to remove certain impurities therein.
For instance, U.S. Pat. No. 3,751,494 is concerned with removing saturated partially-chlorinated hydrocarbons from unsaturated chlorocarbon and chlorinated hydrocarbons including perchlorethylene by treatment with a type 13.times. molecular sieve. The partially-chlorinated hydrocarbons are dechlorinated and the products of dehydrochlorination are at least partially adsorbed. In the process suggested in U.S. Pat. No. 3,751,494, the action of the molecular sieve on the saturated chlorinated hydrocarbons also results in the production of hydrogen chloride.
U.S. Pat. No. 2,888,495 to Kissling suggests purifying perchloroethylene by contacting it with ion exchange resins in order to reduce the acidity of the perchlorethylene composition. U.S. Pat. No. 3,309,166 to Moncada et al. suggests an adsorption for purifying various solvents among which is suggested perchlorethylene. U.S. Pat. No. 3,452,110 is exemplary of those patents which suggest filtering processes for purifying solvents including perchloroethylene.